Resolvers, which have a simpler structure than optical encoders and show little error with temperature change, are widely used as rotation angle detection devices for detecting the rotation angle and rotation speed of a motor generator. However, resolvers are susceptible to the effects of external magnetic flux generated by the motor coil, etc. of the motor generator. Therefore, in order to reduce the effects of external magnetic flux, various structural measures have been devised for the coils of a resolver (see, for example, PTL 1).
In a conventional rotation angle detection device using a resolver of this kind, in order to further reduce the effect of external magnetic flux, the S/N ratio of the induction signal induced in the induction coil of the resolver is improved by raising the amplitude or frequency of the excitation signal which is applied to the excitation coil of the resolver.